Thursday, January 29, 2009

Emperor penguins -- the stars of the 2005 documentary March of the Penguins -- may be headed for a population collapse brought on by global warming, according to a study published this week in the Proceedings of the National Academy of Sciences. The impact of climate change on the extent of sea ice in Antarctica, where the penguins live and breed, is projected to reduce the penguin population by nearly 95% by the end of this century.

The authors of the report developed a sophisticated computer model to predict the population size over time for a specific colony of emperor penguins that currently contains about 6000 breeding pairs. The model was tuned to fit actual observations of a smaller population collapse that occurred during a warm period in the 1970's, and then it was coupled to the predictions of future climate from the Nobel prize-winning report of the Intergovernmental Panel on Climate Change (IPCC). The key factor that determines whether the penguin population will decline over time is how often such warm periods occur -- if they happen too often, the sea ice does not have a chance to recover between events and the penguins suffer a loss of habitat that reduces their chances of survival and corrodes their ability to reproduce.

The population model was coupled to a wide variety of individual climate predictions from the IPCC report, but all of them assumed a "business as usual" scenario in which humans continued to burn fossil fuels sufficient to double the atmospheric concentration of carbon dioxide (CO2) from pre-industrial levels by the end of the century (from 360 to 720 ppm). While this does not represent the worst case scenario for the future climate of our planet, humanity can certainly choose to avoid such a path. For example, most scientists agree that we can avoid the worst consequences of global warming by stabilizing CO2 concentrations no higher than 450 ppm, and the successor to the Kyoto climate treaty is likely to specify this target.

The results of the study suggest that the emperor penguin population could decline by 95% to only 400 breeding pairs by 2100 -- an event that would qualify as a "quasi-extinction". The chances of this happening varied from near certainty (84%) to about 1-in-3 (36%) depending on which specific climate projection was used, but all of them predicted a population in steep decline after 2080. Unlike other Antarctic species, emperor penguin behavior -- such as the timing of their migration and egg laying -- does not appear to have changed much in response to the warming that has already occurred. The authors speculate that the long lives of the penguins may prevent them from adapting to these relatively fast environmental changes, so it is unlikely that they will be able to save themselves.

The good news is that our planet is not yet committed to the amount of warming represented by these projections. We can choose to alter our behavior now, and reduce the future increases in greenhouse gas concentrations below those assumed in this report. If we do, perhaps our grandchildren will one day be able to enjoy March of the Penguins 2.